We are interested in the mechanisms by which RNA tumor viruses replicate and induce neoplastic transformation. The objectives of the proposed study include the elucidation of the biochemical nature of the oncornavirus S70 RNA genome and its transcription into DNA by the oncornavirus RNA-directed DNA polymerase. More specifically, our studies on the oncornavirus genome include an analysis of the interactions responsible for the maintenance and formation of the S70 RNA complex, acquisition of host cell sequences (transduction) by the RNA tumor virus genome during infection, and the possible genetic recombination between two genetically unrelated avian oncornaviruses during mixed infection of avian cells. These studies will be performed by reannealing, hybridization and/or competition hybridization experiments and should reveal information regarding the nature and location of the sequences involved in the formation of S70 RNA, transduction and genetic recombination. Our continuing studies on RNA-directed DNA synthesis include a further analysis of the major species of primer RNA, characterization of additional S70-associated S4 RNAs that can participate as primers, and studies on the efficiency and extent of transcription of the genome RNA into DNA. The latter studies are directed at elucidating the exact requirements needed to transcribe genome RNA into unit length DNA chains in vitro by the RNA-directed DNA polymerase including any requirement for auxillary factors from the host cell to facilitate this transcription. We also plan to continue our studies on the effect, if any of the oncornavirus RNase H activity on the transcription of genome RNA in vitro. Knowledge of the nature of both the oncornavirus genome and the RNA-directed DNA polymerase will be required before an understanding of the precise mechanisms of RNA-directed DNA synthesis and, ultimately proviral DNA synthesis, can be attained.